Lock mechanism for downhole tools

ABSTRACT

Methods and apparatuses used in locking downhole tools such as locking packers, bridge plugs, and frac plugs are shown herein that decrease the loss of energy during pack-off.

CROSS-REFERENCE TO RELATED APPLICATIONS

The priority of U.S. Provisional Application Ser. No. 61/663,737, entitled “Lock Mechanism for Downhole Tools”, filed Jun. 25, 2012, in the name of the inventor William M. Roberts is hereby claimed pursuant to 35 U.S.C. §119(e). This application is also hereby incorporated by reference for all purposes as if set forth herein verbatim.

BACKGROUND

1. Field of the Invention

Embodiments disclosed herein relate to apparatuses and methods used in locking downhole tools. More specifically, embodiments disclosed herein relate to apparatuses and methods used in locking packers, bridge plugs, and frac plugs. More specifically still, embodiments disclosed herein relate to apparatuses and methods used in locking packers, bridge plugs, and frac plugs to decrease the loss of energy during pack-off.

2. Background Art

This section introduces information from the art that may be related to or provide context for some aspects of the technique described herein and/or claimed below. This information is background facilitating a better understanding of that which is disclosed herein. This is a discussion of “related” art. That such art is related in no way implies that it is also “prior” art. The related art may or may not be prior art. The discussion is to be read in this light, and not as admissions of prior art.

In the oilfield industry various downhole tools are used to isolate sections of wellbores. Examples of such tools include packers, bridge plugs, and frac plugs. Typically, when a driller isolates a section of a wellbore, a packer, bridge plug, or frac plug is lowered into the wellbore to a predetermined depth. When the downhole tool reaches the predetermined depth, the tool is actuated, which causes one or more sealing elements to radially expand within the wellbore, thereby isolating a portion of the well below the downhole tool from a portion of the well above the downhole tool.

Traditional downhole tools used in isolating portions of wellbores have various designs, one of which employs one or more lock rings designed to retain pack-off energy in the downhole tool. In certain designs, the lock ring has a double set of threads, where one is a fine pitch and the second is a coarse pitch. During actuation, when the lock ring is pushed into engagement with the mating fine pitch thread, one of several scenarios may occur that results in a loss of pack-off energy.

First, the fine tooth of the female part may not completely pass the fine tooth of the male part, and thus will not bite properly. The female part may then slip back one pitch, or a portion of a pitch, before biting into the male thread. This longitudinal stroke is referred to in the industry as “bounce” and translates to a loss of pack-off energy stored in the element.

Second, as the lock ring moves it is forced to expand and contract as each individual thread moves over a subsequent tooth. When the lock ring bites it is in the contracted state, which allows maximum clearance between the coarse thread forms. The longitudinal movement between the coarse thread forms also results in a loss of pack-off energy.

In certain downhole tool designs, multiple lock rings have been used in the same housing in an attempt to decrease the loss of pack-off energy. By using multiple lock rings, the fine thread of one lock ring will not be at the same place as the fine thread of a second lock ring, thereby effectively splitting the thread and decreasing bounce.

Accordingly, there exists a continuing need for downhole tool actuation apparatuses and methods that have more elective pack-off energy retention and thus higher pressure holding capabilities across a sealing element. The presently disclosed technique is directed to resolving, or at least reducing, one or all of the problems mentioned above. Furthermore, the art is always receptive to improvements or alternative means, methods and configurations.

SUMMARY

In a first aspect, the presently claimed subject matter is directed to a downhole tool comprising: a mandrel; a sealing element disposed around the mandrel; a cone disposed below the sealing element, the cone having a plurality of teeth on the inner diameter of the cone; a slip disposed below the cone; and a bottom sub disposed below the slip.

In a second aspect, the presently claimed subject matter is directed to a method of locking a downhole tool, the method comprising: moving a cone of the downhole tool; collapsing the cone under a slip of the downhole tool; engaging a plurality of teeth on an inner diameter of the cone with an outer diameter of the mandrel; and expanding radially a sealing element.

In a third aspect, the presently claimed subject matter is directed to a method of locking a downhole tool, the method comprising: moving a cone of the downhole tool; collapsing the cone under a slip of the downhole tool; engaging a plurality of teeth on an inner diameter of the cone with a second plurality of teeth on an outer diameter of the mandrel; and expanding radially a sealing element.

The above presents a simplified summary of the present disclosure in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

BRIEF DESCRIPTION OF DRAWINGS

The claimed subject matter may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

FIG. 1 is a cross-sectional side view of a downhole tool according to embodiments of the present disclosure.

FIG. 2 is a cross-sectional side view of a downhole tool in an embodiment alternative to that of FIG. 1.

FIG. 3-FIG. 4 are a plan side and cross-sectional view, respectively, of a mandrel according to the embodiment shown in FIG. 1.

FIG. 5 is a cross-sectional view of a mandrel according to embodiments of the present disclosure.

FIG. 6-FIG. 7 are cross-sectional views of cones according to embodiments of the present disclosure as may be used in implementing, for example, the downhole tools of FIG. 1-FIG. 2.

FIG. 8-FIG. 9 are cross-sectional views of a lock ring retainer and a lock ring, respectively, as may be used to implement the downhole tools in embodiments shown in FIG. 1.

FIG. 10 is a side view of a slip according to embodiments of the present disclosure.

FIG. 11 is a cross-sectional view of a slip according to embodiments of the present disclosure.

While the subject matter claimed below is susceptible to various modifications and alternative forms, the drawings illustrate specific embodiments herein described in detail by way of example. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

One or more specific embodiments of the present invention will be described below. The present invention is not limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the appended claims. In the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

Turning now to the drawings, FIG. 1 is a cross-sectional view of a downhole tool 100. In this embodiment, downhole tool 100 is a frac plug, which is a tool designed to provide isolation between sections of a wellbore during multistage stimulation treatments. Downhole tool 100 includes a mandrel 105. Mandrel 105 may be formed from various metals, such as aluminum, stainless steel, other metal alloys, or in certain embodiments, from various composites, such as fiberglass with epoxy resins. Mandrel 105 has a central flow bore 110, through which fluids may flow after treatment. A lock ring retainer 115 is disposed around the upper end 120 of mandrel 105. The lock ring retainer 115 is configured to retain lock ring 125, which is disposed between lock ring retainer 115 and mandrel 105. Lock ring retainer 115 is threaded along the inner diameter to engage corresponding threads of lock ring 125.

Downhole tool 100 further includes a sealing element 130, which is disposed axially below lock ring 125 on mandrel 105. Sealing element 130 is configured to radially expand, thereby isolating two areas of a well. The sealing element may be formed from various high-pressure/high-temperature elastomeric materials. A sealing element retainer 135 is disposed on mandrel between lock ring 125 and sealing element 130. The sealing element retainer 135 is configured to hold sealing element 130 in place on mandrel 105.

Downhole tool 100 also includes a cone 140 disposed on mandrel 105 axially below sealing element 130. Cone 140 may be formed from a variety of materials including, for example, metals alloys such as stainless steel. Cone 140 includes a plurality of teeth 145 machined along the inner diameter of the cone. The plurality of teeth 145 may include a fine pitch buttress thread form. For example, in certain embodiments, the thread pitch may be approximately 1/16^(th) of an inch. In such a fine pitch buttress thread form, approximately 16 threads may be machined per inch. The plurality of teeth 145 of cone 140 are configured to engage a second plurality of teeth 150 machined onto the outer diameter of mandrel 105. The second plurality of teeth 150 of mandrel 105 may also include a fine pitch buttress thread forms, such as a thread as described above.

Axially above cone 140 and below sealing element 130, a triangle ring 136 and a backup ring 137 may be disposed. Triangle ring 136 may be formed from bakelite and include one or more grooves 138, into which sealing element 130 may be disposed. In certain embodiments, the sealing element 130 and the triangle ring are bonded together. Thus, during actuation, triangle ring 136 is configured to collapse, thereby preventing extrusion of the sealing element 130. A backup ring 137 is disposed axially below triangle ring 136. Backup ring 137 may also be formed from bakelite. Backup ring 137 may include a plurality of notches (not shown) or castellations that are configured to engage a corresponding plurality of notches (not shown) or castellations of the triangle ring 136. Backup ring 137 may further include a second plurality of notches (not shown) or castellations that are configured to engage cone 140. During actuation, the backup ring 137 expands and locks into cone 140. The engagement of sealing element 130, triangle ring 136, backup ring 137, and cone 140 after actuation may enhance drill out operations of downhole tool 100.

Downhole tool 100 further includes one or more slips 155 disposed around mandrel 105 axially below cone 140. In one embodiment, slip or slips 155 may include a cylindrical unibody slip. As illustrated, slip 155 includes a tapered upper portion 160 that extends partially over cone 140. During actuation of downhole tool 100, the cone 140 slides under tapered portion 160. The tapered portion 160 of slip 155 forces cone 140 into contact with mandrel 105. As tapered portion 160 of slip 155 forces cone 140 into contact with mandrel 105, the plurality of teeth 145 of cone 140 engage the second plurality of teeth 150 of mandrel 105. The tapered portion 160 of slip 155 pushes cone 140 into contact with mandrel 105 and the cone 140 collapses inwardly. Because cone 140 collapses into contact with mandrel 105, and the plurality of teeth 150 of the cone 140 engage the second plurality of teeth 150 of mandrel 105, the drillability of downhole tool 100 may be enhanced. Because the components are effectively locked together, the individual components will not slide down until a mill drills out the components.

A bottom sub 165 is disposed axially below slip 155. Bottom sub 165 holds slip 155 in place and includes a threadable connection for attaching downhole tool 100 to other downhole tools, drill pipe, etc. in certain embodiments, downhole tool 100 may further include a ball 170 located in central flow bore 110. Ball 170 may be used to seal the top of mandrel 105, while floating off mandrel 105, thereby not blocking central flow bore 110 when pressure from below is applied.

In an alternative embodiment, second plurality of teeth 150 may not be machined onto mandrel 105. In such an embodiment, during actuation, the plurality of teeth 145 of cone 140 may engage and bite into the mandrel 105, which is formed from a softer material. As the cone 140 moves into contact with upper portion 160 of slip 155, the cone 140 deflects or collapses inwardly, thereby mechanically securing the cone 140 to the mandrel 105, preventing loss of energy. Such an embodiment may be used when no threads are cut into the mandrel 105, such as is common when non-metallic mandrels 105 are used. Those of ordinary skill in the art having the benefit of this disclosure will appreciate that in alternative embodiments, additional slips could be used to further the pressure holding ability of the tool 100.

Referring to FIG. 2, a cross-sectional view of a downhole tool 200 is shown. In this embodiment, downhole tool 200 is a bridge plug, which is a tool designed to provide isolation between sections of a wellbore during multistage stimulation treatments or to permanently seal a portion of a wellbore from production. Downhole tool 200 includes a mandrel 205. Mandrel 205 may be formed from various metal alloys, such as stainless steel, or in certain embodiments, from various composites.

In this embodiment, downhole tool 200 has a first slip 210 disposed on an upper end 215 of mandrel 205. Slip 210 has a tapered portion 220 that is configured to extend over a first cone 225. Cone 225 is disposed axially below slip 210. Downhole tool 200 further includes a sealing element 230, disposed axially below cone 225. As described above with respect to downhole tool 100, cone 225 includes a plurality of teeth 235 machined along the inner diameter of the cone. The plurality of teeth 235 may include a fine pitch buttress thread form. Such as the fine pitch buttress thread form described above. The plurality of teeth 235 of cone 225 are configured to engage a second plurality of teeth 240 machined onto the outer diameter of mandrel 205. The second plurality of teeth 240 of mandrel 205 may also include a fine pitch buttress thread form, such as that disclosed above.

During actuation, the tapered portion 220 of slip 210 presses down on cone 225, thereby causing the plurality of teeth 235 of cone 225 to engage and bite into the second plurality of teeth 240 of mandrel 205. As the plurality of teeth 235 of cone 225 engage the second plurality of teeth 240 of mandrel 205, the cone 225 is mechanically secured to the mandrel 205, thereby lessening the loss of pack-off energy due to bounce.

Axially below cone 225, a sealing element 230 is disposed around mandrel 205. The sealing element 230 may be formed from various high-pressure/high-temperature materials, such as elastomeric materials, and is configured to radially expand.

A second cone 250 is disposed on mandrel 205 axially below sealing element 230. As described above with respect to downhole tool 100, downhole tool 200 further includes a second slip 255 disposed axially below second cone 250. Second cone 250 includes a plurality of teeth 260 machined along the inner diameter of the second cone 250. The plurality of teeth 260 may include a fine pitch buttress thread form. plurality of teeth 260 of second cone 250 are configured to engage a second plurality of teeth 265 machined onto the outer diameter of mandrel 205. The second plurality of teeth 265 of mandrel 205 may also include a fine pitch buttress thread form, such as those described above.

During actuation, a tapered portion 270 of second slip 255 presses down on second cone 250, thereby causing the plurality of teeth 260 of second cone 250 to engage and bite into the second plurality of teeth 265 of mandrel 205. As the plurality of teeth 260 of cone 250 engage the second plurality of teeth 265 of mandrel 205, the second cone 250 is mechanically secured to the mandrel 205, thereby making the tool 100 more stable during drill up. Additionally, as the second cone 250 is secured to the mandrel 205, the mandrel may be prevented from falling out during the drill out process.

As discussed above with respect to downhole tool 100, downhole tool 200 may also include one or more triangle rings 236 and 238 and/or backup rings 237 and 239. In this embodiment, a first triangle ring 236 may be disposed axially above sealing element 230 and a first backup ring 237 may be disposed axially above first triangle ring 236. Similarly, a second triangle ring 238 may be disposed axially below sealing element 230, with a second backup ring 239 disposed axially below second triangle ring 238. During actuation, the triangle rings 236 and 238, as well as the backup rings 237 and 239 of downhole tool 200 may operate substantially the same as the triangle and backup rings discussed with respect to downhole tool 100 of FIG. 1.

A bottom sub 275 is disposed axially below second slip 255. Bottom sub 275 holds slip 255 in place and includes a threadable connection for attaching downhole tool 200 to other downhole tools, such as, for example, additional bridge plugs and/or frac plugs.

In an alternative embodiment, mandrel 205 may not have teeth configured to engage cone 225 or second cone 250. In such an embodiment, the plurality of teeth 235, 265 of cone 225 and second cone 250 may engage or bite directly into mandrel 205. Such an embodiment may be used when no threads are cut into the mandrel 205, such as is common when non-metallic/composite mandrels 205 are used. Those of ordinary skill in the art wilt appreciate that in alternative embodiments, additional slips could be used to further improve the pressure holding capability of the tool 200.

To further explain certain aspects of the present disclosure, individual components of downhole tools disclosed herein are described below.

Referring to FIGS. 3 and 4, plan side and cross-sectional views, respectively, of mandrel 305 of downhole tool 300. In this embodiment, a mandrel 305 for a frac plug is illustrated. Mandrel 305 includes an upper end 310 that has a threadable connection 315, such as a pin, which is commonly used in downhole tools in the oilfield industry. Mandrel 305 includes a central flow bore 320 having a restricted portion 325. Restricted portion 325 may be used as a ball seat. In certain embodiments, a ball (not shown) may be disposed on restricted portion 325 to control the flow of fluids through the central flow bore 320. Those of ordinary skill in the art will appreciate that the precise dimensions of restricted portion 325 may vary based on the requirements of the operation, thus, restricted portions 325 of varying size and geometry may be used.

Mandrel 305 further includes a plurality of teeth 330 machined along the outer diameter of the mandrel 305. The plurality of teeth 330 may include a fine pitch buttress thread form, such as those discussed above. The plurality of teeth 330 may be configured to engage one or more components of downhole tool 300, such as lock rings, which are described above in detail with respect to FIG. 1.

Mandrel 305 further includes a second plurality of teeth 335 machined along the outer diameter of mandrel 305 axially below the first plurality of teeth 330. The second plurality of teeth 335 may include a fine pitch buttress thread form, such as those described above. The second plurality of teeth 335 may be configured to engage a cone of a downhole toot 300 during actuation as described above with respect to FIG. 1 and FIG. 2. In certain embodiments, a second plurality of teeth 335 may not be machined on the outer diameter of mandrel 305. In such an embodiment, a cone of a downhole tool 300 may bite directly into the mandrel 305. Those of ordinary skill in the art will appreciate that mandrel 305 may be formed from various materials including metal alloys, such as stainless steel, or composite materials.

Referring to FIG. 5, a cross-sectional view of a mandrel 505 of a downhole tool 500 according to embodiments of the present disclosure is shown. In this embodiment, a mandrel 505 for a bridge plug is illustrated. Mandrel 505 includes an upper end 510 that has a threadable connection 515, such as a pin, which is commonly used in downhole tools in the oilfield industry.

Mandrel 505 further includes a plurality of teeth 530 machined along the outer diameter of the mandrel 505. The plurality of teeth 530 may include a fine pitch buttress thread form, such as those described above. The plurality of teeth 530 may be configured to engage one or more components of downhole tool 500, such as an upper cone, described above with respect to FIG. 2.

Mandrel 505 further includes a second plurality of teeth 535 machined along the outer diameter of mandrel 505 axially below the first plurality of teeth 530. The second plurality of teeth 535 may include a fine pitch buttress thread form, such as those described above. The second plurality of teeth 535 may be configured to engage a lower cone of a downhole tool 500 during actuation as described above with respect to FIG. 2. In certain embodiments, the first and second plurality of teeth 530, 535 may not be machined on the outer diameter of mandrel 505. In such an embodiment, one or more cones of a downhole tool 500 may bite directly into the mandrel 505. Those of ordinary skill in the art will appreciate that mandrel 505 may be formed from various materials including metal alloys, such as stainless steel, or composite materials.

Referring to FIG. 6 and FIG. 7, cross-sectional views of cones 600, 700 according to embodiments of the present disclosure are shown. In this embodiment, cone 600 is the type of cone that may be used in a frac plug, as described with respect to FIG. 1, or as the lower cone in a downhole tool such as a bridge plug, as described with respect to FIG. 2. Cone 700 is representative of the type of cone that may be used as an upper cone in, for example, a bridge plug. Those of ordinary skill will appreciate that such cones may be used in various downhole applications in addition to frac plugs and bridge plugs. For example, either type of cone may be used in packers as well.

As illustrated, cone 600 includes a plurality of teeth 605 machined along the inner diameter of the cone 600. The plurality of teeth 605 may include a fine pitch buttress thread form, such as those described above. Additionally, cone 600 may include a plurality of ramps 610, rather than constitute a single conical surface. Thus, a plurality of teeth 605 may be machined along the inner diameter of each ramp 610. The plurality of teeth 605 may be machined to correspond to a plurality of teeth that are machined along an outer diameter of a mandrel of a downhole tool, as described above. However, in certain embodiments, the plurality of teeth 605 may be machined along the inner diameter of cone 600 to engage directly with a mandrel of a downhole tool.

Similarly, cone 700 also includes a plurality of teeth 705 machined along the inner diameter of the cone 700. The plurality of teeth 705 may include a fine pitch buttress thread form, such as those described above. Additionally, cone 700 may include a plurality of ramps 710, rather than constitute a single conical surface. Thus, a plurality of teeth 705 may be machined along the inner diameter of each ramp 710. The plurality of teeth 705 may be machined to correspond to a plurality of teeth that are machined along an outer diameter of a mandrel of a downhole tool, as described above. However, in certain embodiments, the plurality of teeth 705 may be machined along the inner diameter of cone 700 to engage directly with a mandrel of a downhole tool.

Depending on the operational requirements, the materials used to form cones 600, 700 may vary. For example, in certain embodiments, cones 600, 700 may be formed from metals and metal alloys, such as aluminum or stainless steel.

FIG. 8 and FIG. 9 are cross-sectional views of a lock ring retainer 800 and a lock ring 900, respectively, such as may be used to implement the downhole tools disclosed above. FIG. 8 illustrates a lock ring retainer 800, which is configured to hold a lock ring 900 in place. Lock ring retainer 800 includes a plurality of teeth 805 along the inner diameter of the lock ring retainer 800. The plurality of teeth 805 is configured to engage a plurality of teeth 905 along the outer diameter of the lock ring 900. During assembly, the lock ring 900 is screwed into lock ring retainer 800, and the assembly is slid into place along a mandrel of a downhole tool, as described in detail above.

In addition to the plurality of teeth 905 along the outer diameter of lock ring 900, lock ring 900 further includes a plurality of teeth 910 along the inner diameter of the lock ring 900. The plurality of teeth 910 along the inner diameter of the lock ring 900 may include a fine pitch buttress thread form, such as those described above. The plurality of teeth along the inner diameter of the lock ring 900 is configured to engage a corresponding set of teeth disposed along the outer diameter of a mandrel of a downhole tool.

Lock ring retainer 800 and lock ring 900 may be formed from various metals and metal alloys, such as, for example, cast iron or stainless steel. Those of ordinary skill in the art will appreciate that the specific materials used to form lock ring retainer 800 and lock ring 900 may vary according to operational considerations.

Referring to FIG. 10 and FIG. 11, side and cross-sectional views of a slip 1000 such as may be used to implement the downhole tools disclosed above. In this embodiment, slip 1000 includes a tapered portion 1005 that is configured to contact a cone of a downhole tool, as described above. The angle of tapered portion 1005 may vary depending on the specific requirements of an operation. For example taper angles that range between 10° and 45°, or in a particular embodiment a taper angle of about 15°, may be used. Slip 1000 may be formed from various materials such as metals and metal alloys, for example, aluminum or stainless steel. In certain embodiments, the outer diameter of the slip 1000 may include a non-slip surface that may be coated in, for example, a carbide material.

Downhole tools according to the disclosure provided above may be actuated in a variety of ways. For example, hydraulic and mechanical actuators such as are known in the art may be used in order to set or radially expand, the sealing elements of frac plugs, bridge plugs, packers, and the like. While the specific actuation mechanisms are known in the art, methods for setting and holding downhole tools in place, according to embodiments of the present disclosure, are described in detail below.

According to one method, after a downhole tool including a cone having a plurality of teeth that are configured to engage the mandrel of the downhole tool is run in hole, the cone of the downhole tool is moved downward. The cone may then collapse under a slip, which causes the plurality of teeth on the cone to engage and bite into the outer diameter of the mandrel. As the teeth of the cone engage the outer diameter of the mandrel a sealing element radially expands. The teeth of the cone may then secure the sealing element in an expanded condition, thereby isolating sections of a wellbore.

In certain embodiments, such as when used in a bridge plug, a second cone having a second plurality of teeth may also collapse under a slip. The teeth of the second cone may also engage or bite into the mandrel, thereby securing the sealing element in an expanded condition from both sides of the sealing element.

In an alternative embodiment, a downhole tool having a cone including a plurality of teeth that are configured to engage a set of corresponding teeth on the outer diameter of a mandrel is run in hole. The cone is then moved, causing the cone to collapse under a slip. As the slip presses down on the cone, the plurality of teeth of the cone engages the plurality of teeth on the outer diameter of the mandrel. The sealing element radially expands and the teeth of the cone engaging the teeth of the mandrel hold the sealing element in an expanded condition. The engagement between the plurality of teeth and the cone may further hold the mandrel in place during drill out, thereby preventing the mandrel from falling downhole.

As described above, in certain embodiments, such as when used in a bridge plug, a second cone having a second plurality of teeth may also collapse under a slip. The teeth of the second cone may also engage or bite into a second set of teeth disposed on the outer diameter of the mandrel, thereby securing the sealing element in an expanded condition from both sides of the sealing element.

Various embodiments of the present disclosure may provide frac plugs, bridge plugs, packers, and the like, which increase a tools pressure-holding capability across a sealing element. Conventional downhole tools employ the interaction of one coarse and one fine threaded component, which results in bounce and a loss in pack-off energy, as described above. Embodiments of the present disclosure collapse the cone under a slip, thereby causing the cone to engage or bite onto corresponding mandrel threads or directly onto the mandrel surface. By collapsing the cone to engage the mandrel, pack-off energy loss due to bounce is reduced. By using fine pitch threads, instead of course threads as are typically used, the lateral movement caused by slack between the coarse threads is decreased, thereby increasing the pack-off energy.

While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the disclosure should be limited only by the attached claims. 

What is claimed:
 1. A downhole tool comprising: a mandrel; a sealing element disposed around the mandrel; a cone disposed below the sealing element, the cone having a plurality of teeth on the inner diameter of the cone; a slip disposed below the cone; and a bottom sub disposed below the slip.
 2. The downhole tool of claim 1, wherein the mandrel further comprises a plurality of teeth on the outer diameter of the mandrel.
 3. The downhole tool of claim 2, wherein the plurality of teeth on the inner diameter of the cone are configured to bite into the plurality of teeth on the outer diameter of the mandrel.
 4. The downhole tool of claim 2, wherein the plurality of teeth on the inner diameter of the cone and the plurality of teeth on the outer diameter of the mandrel comprise fine pitch buttress threads.
 5. The downhole tool of claim 1, further comprising a backup ring disposed between the sealing element and the cone.
 6. The downhole tool of claim 1, wherein the plurality of teeth on the inner diameter of the cone are configured to bite into the outer diameter of the mandrel.
 7. The downhole tool of claim 1, wherein the cone is configured to collapse under the slip.
 8. The downhole tool of claim 1, further comprising a second cone disposed above the sealing element, wherein the second cone comprises a plurality of teeth on the inner diameter of the second cone.
 9. The downhole tool of claim 8, wherein the mandrel further comprises a second plurality of teeth on the outer diameter of the mandrel, wherein the second plurality of teeth on the outer diameter of the mandrel are configured to mate with the plurality of teeth on the inner diameter of the second cone.
 10. The downhole tool of claim 1, further comprising a ball disposed in the mandrel.
 11. A method of locking a downhole tool, the method comprising: moving a cone of the downhole tool; collapsing the cone under a slip of the downhole tool; engaging a plurality of teeth on an inner diameter of the cone with an outer diameter of the mandrel; and expanding radially a sealing element.
 12. The method of claim 11, further comprising collapsing a second cone of the downhole tool under a second slip.
 13. The method of claim 12, further comprising engaging a second plurality of teeth on the inner diameter of the second cone with the outer diameter of the mandrel.
 14. The method of claim 11, wherein the plurality of teeth comprises a fine pitch buttress thread form.
 15. The method of claim 11, further comprising engaging a backup ring to the cone.
 16. A method of locking a downhole tool, the method comprising: moving a cone of the downhole tool; collapsing the cone under a slip of the downhole tool; engaging a plurality of teeth on an inner diameter of the cone with a second plurality of teeth on an outer diameter of the mandrel; and expanding radially a sealing element.
 17. The method of claim 16, further comprising collapsing a second cone of the downhole tool under a second slip.
 18. The method of claim 17, further comprising engaging a plurality of teeth on an inner diameter of the second cone with a third plurality of teeth on the outer diameter of the mandrel.
 19. The method of claim 16, wherein the plurality of teeth comprises a fine pitch buttress thread form.
 20. The method of claim 16, further comprising engaging a backup ring with the cone. 